Receiver tuning circuits



Feb. 15, 1938. I c. J. VAN LOON 2,108,154

RECEIVER TUNING CIRCUITS Filed July 30, 1936 ams/e KNOB FREQUENCY c e d3 9 r0 1. F. AMPUF/ERH 4 /2 T DC- v INVENTOR CAREL JAN VAN LOON BY I v MATTORNEY vention is, however, primarily intended for a amplification ofthe low-frequency oscillations the accompanying drawing.

Patented Feb. 15, 1938 UNITED STATES PATENT 'QFFICE RECEIVER TUNINGCKRCUITS Application July 30, 1936, Serial No. 93,354 In Germany October26, 1935 11 Claims. (01. 250-40) This invention relates to a circuitarrangement grid 2 of a pentode 3. The screening grid is for assistingthe tuning of wireless receiving sets. connected to a point of aresistance I8 by which Such arrangements are particularly desirable forthe voltage supply leads are bridged. The cathsets having automaticvolume control, since in ode is connected to the negative conductor bythis case it is often very difficult for laymen to way of a resistancewhich provides negative grid find the point of correct tuning. Thecircuit bias. The output circuit of the valve includes a arrangementaccording to the invention serving circuit 4 which comprises aninductance and a for assisting tuning is set into operation uponcapacity and which may be tuned to the interaccurately tuning to thedesired carrier wave. mediate frequency, although as an alternative anThe tuning may be assisted, for example, in that aperiodic circuit maybe used. The voltage acan optical device is set into operation upon thetive in the output circuit is supplied via a concorrect tuning beingreached, or in that not until denser 5 to a rectifier B, l which jointlywith two this moment the low frequency amplifier part of resistances 2 band I3 constitutes a closed direct the set is caused to becomeoperative. The incurrent circuit. The output circuit of the tube 3 is inaddition coupled via the condenser 8 to a circuit 9 of low damping tunedto the intermediate frequency carrier wave. The voltages occurring inthis circuit are supplied to the rectifier i, H, and bring about avoltage drop across the resistances i2 and H3 in such manner that theupper point of the resistance l2 becomes negative relatively to thelower.

The two rectifiers may be separated from each other, but preferably, asshown in Fig. 1, they are housed in a single bulb and have one commoncathode. As shown in Fig. 1, the resist ance I3 is included in bothrectifier circuits. The resistance it constitutes the input circuit of arectifier valve M, the output circuit of which includes a magneticbraking device I5 which, as will be described hereinafter, prevents anyfurther movement of the tuning knob ll upon the correct tuning of thelatter to a carrier wave. For this purpose, the shaft of the knob hasmounted on it a braking disc it of soft iron. Instead of using amagnetic braking device, it is also possible to use an electrostaticalone.

The device operates as follows:

When the grid of the tube 3 has not supplied to it signal voltages,neither of the two rectifiers carries current and the grid of the valveM has such a potential that a current fiows in the anode circuit. Themagnetizing effect of this current is neutralized by a constant currentpassing through a second coil H5, or by a permanent magnet, so that thetuning knob can be moved freely. Now, when approaching to the point ofcorrect tuning, a voltage first occurs through the circuit 4 so that arectified current flows through the resistances 24 and I3. The voltagedrop across the resistance !3 is such that the upper point of thisresistance becomes positive relatively to the lower one. Whenapproaching still more to the correct tuning, a voltage will also occuracross the second circuit 9. Due to the device in which upon correcttuning further rotation of the tuning member is prevented, for example,by a brake being brought into operation.

According to the invention, two rectifiers are coupled to thehighfrequency or intermediatefrequency amplifier in such a manner thatone of the rectifiers is preceded by greater selectivity than the other.In addition, the rectifiers are connected in such a manner that therectifier voltage of one rectifier influences the other in such a mannerthat this latter rectifies only in the immediate vicinity of theresonance frequency and that the rectified current of this rectifier isused for the control of the device by which tuning is assisted.

Preferably, the part of the receiving set that assists tuning solelyserves this purpose and rectification of the high-frequency oscillationsand are effected by other valves separated therefrom.

The circuit arrangement is preferably arranged in such manner that thedirect current of the rectifier which is preceded by the greatestselectivity brings about the control.

In order that the invention may be clearly understood and readilycarried into effect a circuit arrangement of this kind will be describedhereinafter, by way of example, with reference to In the drawing:

Fig. 1 shows a circuit diagram of one form of the invention,

Fig. 2 graphically shows the operation of the invention, and

Fig. 3 shows a modified form of the invention.

In the circuit arrangement shown in Figure l the voltage of anintermediate frequency amplifier stage (not shown) of the receiving setis supplied through a condenser I to the control voltage drop across theresistance 13, which is also active in the second rectifier circuit, acurrent will not flow in the second rectifier circuit until thealternating voltage active across the circuit 9 has an amplitude whichexceeds the value of the voltage across the resistance l3.

This action is illustrated in Figure 2 by means of a few curves. Thecurve (1. represents the voltage across the resistance l3 as a functionof the frequency of the arriving signal. The point 6 corresponds to theresonance frequency of the circuit 4. The curve 1) represents thevoltage across the circuit 9 as a function of the frequency. It isobvious that the rectifier I, II is not caused to become operative untilthis voltage exceeds the voltage across the resistance l3, consequently,when in tuning a frequency corresponding to one of the points 0 or d isreached. Not until then has the resistance [2 occurring through it apotential drop which applies such a bias to the tube [4 that the brakeis set into operation. It is easy so to proportion the circuit 9 thatthe device is set into operation at a frequency which differs verylittle for example by a few hundred cycles, from the natural frequencyof the circuit 9.

In the circuit arrangement described it is ensured that the action ofthe brake is practically independent of the intensity of the signalvoltage and the adjustment is but slightly critical. The tube M can beconnected so that the anode current increases upon the arrival of asignal. In this case, the second coil on the magnet core of the brakecan be dispensed with. The control voltage for the braking device mayalso be derived from a further resistance, for example I2, since it canbe obtained by adequate proportioning that the current of the rectifierpath 6-1 ceases when the current across the second path attains a givenvalue. Numerals iii and I9 denote appropriate I. F. bypass condensers.

Figure 3 shows a slightly different circuit arrangement which diifersfrom that shown in Figure 1 in that the valve 3 also serves as a brakingvalve. For this purpose the voltage active across the resistance I2 isled back to the control grid of this valve, and the braking device 15 isincluded in the anode circuit of this valve. Thus a saving of one tubeis obtained. In this circuit arrangement it is desirable to provide adevice that limits the voltage active in the output circuit of the valve3. A glow discharge lamp 20 is provided for this purpose. The resistance23 as well as the condenser 2i serve for smoothing the voltage led back.The resistance 22 is the input resistance for the grid of the valve 3.

What is claimed is:

1. In combination with the adjustable tuner element of a radio receiver,means to control adjustment of the tuner element, a control network forsaid means comprising a pair of rectifiers, a resonant signal inputcircuit, tuned to a desired signal frequency, coupled to one rectifier,a second signal input circuit, tuned to said desired frequency coupledto the second rectifier, the selectivity at the second circuit beinggreater, means for impressing signals on said signal circuits, meansresponsive to current flow in said one rectifier for preventing currentflow in the second rectifier until the signal amplitude at the secondinput circuit attains a desired value, and means responsive to currentflow in the second rectifier for controlling the operation of said firstmeans.

2. In combination with the adjustable tuner element of a radio receiver,means to control adjustment of the tuner element, a control network forsaid means comprising a pair of rectifiers, a resonant signal inputcircuit, tuned to a desired signal frequency, coupled to one rectifier,a second signal input circuit, tuned to said desired frequency coupledto the second rectifier, the selectivity at the second circuit beinggreater, means for impressing signals on said signal circuits, meansresponsive to current flow in said one rectifier for preventing currentflow in the second rectifier until the signal amplitude at the secondinput circuit attains a desired value, and means responsive to currentflow in the second rectifier for controlling the operation of said firstmeans, said tuner control means comprising a magnetic brake deviceconstructed to prevent adjustment of the tuner element when energized.

3. In combination with the adjustable tuner element of a radio receiver,means to control adjustment of the tuner element, a control net- Workfor said means comprising a pair of rectifiers, a resonant signal inputcircuit, tuned to a desired signal frequency, coupled to one rectifier,a second signal input circuit, tuned to said desired frequency coupledto the second rectifier, the selectivity at the second circuit beinggreater, means for impressing signals on said signal circuits, meansresponsive to current fiow in said one rectifier for preventing currentflow in the second rectifier until the signal amplitude at the secondinput circuit attains a desired value, means responsive to current flowin the second rectifier for controlling the operation of said firstmeans, said signal impressing means including an amplifier, and saidamplifier also being included in said last named responsive means.

4. In combination with the adjustable tuner element of a radio receiver,means to control adju'stment of the tuner element, a control network forsaid means comprising a pair of rectifiers, a resonant signal inputcircuit, tuned to a desired signal frequency, coupled to one rectifier,a second signal input circuit, tuned to said desired frequency coupledto the second rectifier, the selectivity at the second circuit beinggreater, means for impressing signals on said signal circuits, meansresponsive to current flow in said one rectifier for preventing currentflow in the second rectifier until the signal amplitude at the secondinput circuit attains a desired value, means responsive to current flowin the second rectifier for controlling the operation of said firstmeans, said tuner control means comprising a magnetic brake device, andsaid controlling means including a tube in Whose space current circuitis connected said brake device.

5. In combination with the adjustable tuner element of a radio receiver,means to control adjustment of the tuner element, a control network forsaid means comprising a pair of rectifiers, a resonant signal inputcircuit, tuned to a desired signal frequency, coupled to one rectifier,a second signal input circuit, tuned to said desired frequency coupledto the second rectifier, the selectivity at the second circuit beinggreater, means for impressing signals on said signal circuits, meansresponsive to current fiow in said one rectifier for preventing currentflow in the second rectifier until the signal amplitude at the secondinput circuit attains a desired value, means responsive to current flowin the second rectifier for controlling the operation of said firstmeans, said signal impressing means and controlling means both includinga common amplifier tube.

6. In combination with the adjustable tuner element of a radio receiver,means to control adjustment of the tuner element, a control network forsaid means comprising a pair of rectifiers, a resonant signal inputcircuit, tuned to a desired signal frequency, coupled to one rectifier,a second signal input circuit, tuned to said desired frequency coupledto the second rectifier, the selectivity at the second circuit beinggreater, means for impressing signals on said signal circuits, meansresponsive to current flow in said one rectifier for preventing currentflow in the second rectifier until the signal amplitude at the secondinput circuit attains a desired value, means responsive to current flowin the second rectifier for controlling the operation of said firstmeans, and a signal amplitude limiter connected across said firstresonant input circuit.

'7. In combination with the adjustable tuner element of a radioreceiver, means to control adjustment of the tuner element, a controlnetwork for said means comprising a pair of rectifiers, a resonantsignal input circuit, tuned to a desired signal frequency, coupled toone rectifier, a second signal input circuit, tuned to said desiredfrequency coupled to the second rectifier, the selectivity at the secondcircuit being greater, means for impressing signals on said signalcircuits, means responsive to current fiow in said one rectifier forpreventing current flow in the second rectifier until the signalamplitude at the second input circuit attains a desired value, and meansresponsive to current flow in the second rectifier for controlling theoperation of said first means, said tuner element having a metallicmember operatively associated therewith, said adjustment control meansincluding a device which acts as a magnet on said member when energized.

8. In combination with the adjustable tuner element of a radio receiver,means to control adjustment of the tuner element, a control network forsaid means comprising a pair of rectifiers, a resonant signal inputcircuit, tuned to a desired signal frequency, coupled to one rectifier,a second signal input circuit, tuned to said desired frequency coupledto the second rectifier, the selectivity at the second circuit beinggreater, means for impressing signals on said signal circuits, meansresponsive to current fiow in said one rectifier for preventing currentflow in the second rectifier until the signal amplitude at the secondinput circuit attains a desired value, means responsive to current fiowin the second rectifier for controlling the operation of said firstmeans, and each of said rectifiers being a diode, the diodes having acommon cathode.

9. In combination with the adjustable station tuning element'of asuperheterodyne receiver, an intermediate frequency energy network, arectifier coupled thereto to rectify signal energy in said network, asecond rectifier having an intermediate frequency input circuit whichhas a higher degree of selectivity than the first network, means forcoupling the latter to said second rectifier input circuit, meansresponsive to current flow in the first rectifier for preventingrectification by the second rectifier until the signal amplitude at theinput circuit thereof exceeds a predetermined amplitude, and meansresponsive to the rectified current output of the second rectifier forpreventing adjustment of said tuning element.

10. In combination with the adjustable station tuning element of asuperheterodyne receiver, an intermediate frequency energy network, arectifier coupled thereto to rectify signal energy in said network, asecond rectifier having an intermediate frequency input circuit whichhas a higher degree of selectivity than the first network, means forcoupling the latter to said second rectifier input circuit, meansresponsive to current flow in the first rectifier for preventingrectification by the second rectifier until the signal amplitude at theinput circuit thereof exceeds a predetermined amplitude, meansresponsive to the rectified current output of the second rectifier forpreventing adjustment of said tuning element, an amplifier includingsaid network in its space current circuit, and said amplifier beingincluded in said last named means.

11. In combination with the adjustable station tuning element of asuperheterodyne receiver, an intermediate frequency energy network, arectifier coupled thereto to rectify signal energy in said network, asecond rectifier having an intermediate frequency input circuit whichhas a higher degree of selectivity than the first network, means forcoupling the latter to said second rectifier input circuit, meansresponsive to current fiow in the first rectifier for preventingrectification by the second rectifier until the signal amplitude at theinput circuit thereof exceeds a predetermined amplitude, and meansresponsive to the rectified current output of the second rectifier forpreventing adjustment of said tuning element, said last means includingan electron discharge tube whose input electrodes are energized by thesecond rectifier current output.

CAREL JAN VAN LOON.

